On certain aircraft such as commercial airliners, tankers, airlifters and transport aircraft, aircraft engines are typically mounted in nacelles that extend from pylons under the wing. In many aircraft, the leading edge of the engine nacelle is positioned forward of the wing leading edge. At high angles of attack, the engine nacelle sheds a wake. For aircraft where the engine nacelles are spaced at a relatively large distance from the wing, the wake generated may pass underneath the wing.
However, for installations where the engine nacelle is mounted in close proximity to the wing, the nacelle wake may flow over the wing leading edge and along the upper wing surface. Although the nacelle wake can be aerodynamically favorable under certain flight conditions, at high angles of attack close to the stalling angle where maximum lift is typically achieved, the nacelle wake can cause flow separation along the upper surface of the wing. Such flow separation may result in a reduction in the amount of lift that is producible by the wing in comparison to what might be achievable absent the nacelle wake.
Aircraft manufacturers have addressed the above-described flow separation phenomenon by installing various vortex-generating devices such as chines on the outer surface of the engine nacelle. The nacelle chine is typically mounted on a side of the engine nacelle and is sized and positioned to control the separation of the nacelle wake by generating a vortex that interacts beneficially with the wing upper surface boundary layer in order to reduce flow separation.
Although effective in improving wing lift capacity at high angles of attack, nacelle chines as conventionally installed possess certain deficiencies which detract from their overall utility. For example, because conventional nacelle chines are fixed in place and because they extend outwardly into the air flow, they produce unwanted aerodynamic drag and can have an adverse impact on the operating efficiency of the aircraft during cruise, takeoff and landing.
A further deficiency associated with conventionally-mounted nacelle chines is related to community noise that is generated by an aircraft which may be especially noticeable during the landing portion of a flight. For example, because the nacelle chine increases drag, engine thrust must be increased accordingly in order to maintain the same approach path. As is well known, community noise is a significant concern among populated areas near an airport. Any increase in aerodynamic drag on an aircraft can increase the community noise around airports.
As can be seen, there exists a need in the art for a nacelle chine that is configured to generate a vortex at high angles of attack for favorably interacting with the wing upper surface boundary layer in order to delay stall. Furthermore, there exists a need in the art for a nacelle chine wherein the contribution to aerodynamic drag is either minimized or eliminated during low angle-of-attack portions of flight. Finally, there exists a need in the art for a nacelle chine that is simple in construction, low in cost and requiring minimal time for installation and maintenance.